The etiologic agents of dermatophytosis are classified, along with some nonpathogenic relatives, in the anamorphic genera Trichophyton, Microsporum, and Epidermophyton. The recorded connections between the teleomorphic (sexual) and anamorphic (asexual) states of the dermatophytes as well as the dermatophytoids are discussed in this chapter. As part of the ongoing molecular revolution in biology, fungal taxonomy is ever more strongly influenced by one's greatly increased understanding of population genetics. The chapter retains a relatively cautious approach to the ongoing debates in this area and synonymizes traditionally recognized species primarily when there is unequivocal, multigene molecular evidence that they are not supported at the species level. Dermatophytes are keratinophilic fungi that are capable of invading the keratinous tissues of living animals. They are grouped into three categories based on host preference and natural habitat. Infections with geophilic dermatophytes involve transmission of soil-borne inoculum to humans or other mammals. At present, the great majority of dermatophytes are identified phenotypically. Identification is often based on (i) colony characteristics in pure culture on sabouraud glucose agar (SGA) and (ii) microscopic morphology. Dermatophytes can in principle be tested for susceptibility to antifungal drugs using the Clinical and Laboratory Standards Institute (CLSI) M38-A3 standard procedure for molds. In the superficial mycoses, the causative fungi colonize the cornified layers of the epidermis or the suprafollicular portion of the hair. There is little tissue damage, and lack in cellular response from the host.

14.Beifuss, B.,, G.Bezold,, P.Gottlöber,, C.Borelli,, J.Wagener,, M.Schaller,, and H. C.Korting. 2011. Direct detection of five common dermatophyte species in clinical samples using a rapid and sensitive 24-h PCR-ELISA technique open to protocol transfer. Mycoses54:137–145.

115.Summerbell, R. C.,, I.Weitzman,, and A.Padhye. 2002. The Trichophyton mentagrophytes complex: biological species and mating type prevalences of North American isolates, and a review of the worldwide distribution and host associations of species and mating types. Stud. Mycol. 47:75–86.

116.Taplin, D.1965. The use of gentamicin in mycology. J. Investig. Dermatol.45:549–550.

117.Taplin, D.,, N.Zaias,, G.Rebell,, and H.Blank. 1969. Isolation and recognition of dermatophytes on a new medium (DTM). Arch. Dermatol. 99:203–209.

a Only the growth responses for organisms with growth factor requirements and the selected organisms that must be most closely compared with them are included in this table. The numbers in the table body indicate the relative degree of growth according to traditional 1+ to 4+ visually approximated scale: 0, no growth; 1, slight growth, strongly nutrient deprived colony morphology (very sparse, subsurface colonial growth only or colony diameter strongly reduced compared to Sabouraud agar control); 2, partially stimulated growth but still significantly suppressed compared to that of the control; 4, growth comparable to that of the control (the table includes no 3+ reactions); v, variable. Blank spaces in the table indicate growth responses that are not customarily examined but that are insignificantly different from control growth responses on Sabouraud agar.

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TABLE 4

a Only the growth responses for organisms with growth factor requirements and the selected organisms that must be most closely compared with them are included in this table. The numbers in the table body indicate the relative degree of growth according to traditional 1+ to 4+ visually approximated scale: 0, no growth; 1, slight growth, strongly nutrient deprived colony morphology (very sparse, subsurface colonial growth only or colony diameter strongly reduced compared to Sabouraud agar control); 2, partially stimulated growth but still significantly suppressed compared to that of the control; 4, growth comparable to that of the control (the table includes no 3+ reactions); v, variable. Blank spaces in the table indicate growth responses that are not customarily examined but that are insignificantly different from control growth responses on Sabouraud agar.

Sequence of procedures for phenotypic identification of dermatophytes in pure culturea

a It may be necessary to incubate cultures on brain-heart infusion agar or BCPMSG to ensure absence of antibiotic-resistant bacterial contamination before proceeding to step 4. Procedures are adapted from Weitzman and colleagues (125) and Kane et al. (66).

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TABLE 5

Sequence of procedures for phenotypic identification of dermatophytes in pure culturea

a It may be necessary to incubate cultures on brain-heart infusion agar or BCPMSG to ensure absence of antibiotic-resistant bacterial contamination before proceeding to step 4. Procedures are adapted from Weitzman and colleagues (125) and Kane et al. (66).